[PATCH V2] bpf: task_group_seq_get_next: cleanup the usage of get/put_task_struct

Oleg Nesterov
2023-08-22T12:06:44Z

get_pid_task() makes no sense, the code does put_task_struct() soon after.
Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill
put_task_struct(), this allows to do get_task_struct() only once before
return.

While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)"
block, this matches the next usage of find_pid_ns() + get_pid_task() in
this function.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
---
kernel/bpf/task_iter.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 4d1125108014..1589ec3faded 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -42,9 +42,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
if (!*tid) {
/* The first time, the iterator calls this function. */
pid = find_pid_ns(common->pid, common->ns);
- if (!pid)
- return NULL;
-
task = get_pid_task(pid, PIDTYPE_TGID);
if (!task)
return NULL;
@@ -66,17 +63,12 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
return task;
}

- pid = find_pid_ns(common->pid_visiting, common->ns);
- if (!pid)
- return NULL;
-
- task = get_pid_task(pid, PIDTYPE_PID);
+ task = find_task_by_pid_ns(common->pid_visiting, common->ns);
if (!task)
return NULL;

retry:
next_task = next_thread(task);
- put_task_struct(task);

saved_tid = *tid;
*tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
@@ -88,7 +80,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
return NULL;
}

- get_task_struct(next_task);
common->pid_visiting = *tid;

if (skip_if_dup_files && task->files == task->group_leader->files) {
@@ -96,6 +87,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
goto retry;
}

+ get_task_struct(next_task);
return next_task;
}

--
2.25.1.362.g51ebf55